Program in Molecular Medicine
First Thesis Advisor
Michael P. Czech, PhD
Inflammation, Obesity, Adipose Tissue, CD40 Antigens
Dissertations, UMMS; Inflammation; Obesity; Adipose Tissue; Antigens, CD40
Obesity results from expansion of white adipose tissue. The inability of white adipose tissue to adequately store lipids leads to ectopic deposition of lipids in non-adipose tissue that can lead to systemic insulin resistance. It is well known that insulin resistance correlates with inflammation of adipose tissue in obese animals and humans. Decreasing inflammation in the adipose tissue has been proven as a therapeutic strategy for improvement of insulin sensitivity in vivo. Numerous factors secreted by immune cells, including macrophages, have been suggested as regulating adipose tissue insulin sensitivity.
In the first part of my thesis, I describe the role of one such factor, CD40 in adipose tissue inflammation. The CD40-CD40L dyad acts as co-stimulation in the interaction of antigen-presenting cells, such as macrophages and dendritic cells, with effector cells, such as T cells, in adaptive immunity. We found that CD40 knockout mice were smaller but surprisingly more insulin resistant and glucose intolerant compared to wild-type mice when fed a high fat diet. Consistent with their metabolic phenotype, knockout mice displayed increased adipose tissue inflammation with infiltration of immune cells including macrophages and T cells. Consistent with increased inflammation, CD40 knockout adipose tissue displayed decreased lipid storage. Deficiency of CD40 also led to increased lipid deposition in liver, which may be due to increased lipid release into circulation from the adipose tissue as well as increased lipid synthesis in the liver. CD40 knockout mice had increased hepatic insulin resistance and increased gluconeogensis despite decreased hepatic inflammation. These findings suggest that CD40 is a novel regulator of adipose tissue inflammation in diet-induced obesity.
In the second part of this thesis we examined perivascular adipose tissue and brown adipose tissue for the presence of inflammation. In contrast to visceral adipose tissue, macrophage infiltration was absent in perivascular and brown adipose tissue as defined by reduced F480+ cells by flow cytometry and immunohistochemistry. We also found that perivascular adipose tissue was similar to brown adipose tissue as shown by gross morphology and gene expression pattern. Inflammatory gene expression was not increased in brown or perivascular adipose tissue in obese mice as determined by microarray gene expression analysis. These findings suggest that perivascular adipose tissue is more similar to brown adipose tissue than white adipose tissue and that both perivascular and brown adipose tissue are resistant to inflammation.
We conclude that, (1) CD40 protects against adipose tissue inflammation in diet-induced obesity, (2) the CD40 knockout mouse is an interesting model of hepatic steatosis with decreased inflammation and (3) perivascular adipose tissue is almost identical to brown adipose tissue in obese mice and that both are resistant to inflammation.
Kogan, S. Role of Inflammation in Diet-Induced Obesity: A Dissertation. (2013). University of Massachusetts Medical School. GSBS Dissertations and Theses. Paper 647. DOI: 10.13028/M2760C. http://escholarship.umassmed.edu/gsbs_diss/647
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